The Electric Arc Spray Manufacture of Rapid Production Tooling: A Case Study

The manufacture of tooling using the electric arc spray process to spray steel directly onto a master pattern offers substantial reductions in the lead times required to make complex tooling for polymer injection moulding and other applications. The process of spray forming is fast, efficient, and low cost, and has been shown to be dimensionally accurate with proper control over the residual stresses that develop during spraying. Poor dimensional control because of high internal stresses in thick arc sprayed steel coatings is well known, but these problems can be avoided by the use of correct spraying conditions. This paper describes the STD SPRAYFORM process for the manufacture of tooling for the polymer injection moulding of a component for a leading company in the U.S. The steps in the spray forming process, both before and after spraying, are described. The spray forming route competed directly with a traditional method for toolmaking and considerably reduced the lead time from order to completion. The tooling produced by spray forming has been operating commercially in production in the U.S. and has to date produced in the region of half a million parts without appreciable wear. The incorporation of contoured cooling channels during spraying has enabled plastic injection moulding cycle times to be decreased by 15%.